No one would imagine that the guitar, probably the most popular instrument in today’s world, is any way endangered. But German-born, New York-based Hans Tammen uses that term to describe his instrument, which involves a standard guitar that also functions as controller for live sound processing. These duo CDs outline his interaction with Dom Minasi, who plays what could probably be called a non-imperiled six-string; or Denman Maroney, whose so-called hyperpiano playing involves using different implements to strike the prepared strings to produce unexpected timbres,.

During the course of 11 tracks, Maroney and Tammen produce a cacophony of unique sounds which bubble and bustle with barely contained exuberance. The pianist’s plucks, scrubs and slides not only propel abrasive timbres that are fascinatingly distinctive, but when he uses the full keyboard, usually in tandem with the preparations, the results ring with thickened authority. For his part Tammen’s usual game plan is outlining spindly and focused themes, often with bottleneck guitar-like stabs, while tremolo pulses from his guitar-extensions provide the ostinato for the performances.

Even though computer oscillations and string quivers permeate all the tracks, the two instruments’ interfaces can be radically varied. For instance compare “Shaman” and “Ornamental”. The former begins with what could be a parody of portentous piano chording straight from an impressionistic recital. Almost immediately however the ostentatious cadenzas are slashed by knife-style guitar slices. As Tammen further unsettles the interface with electronically oriented watery pulsations, tremolo crackles what could be tin foil crumbling, Maroney responds with whining plucks and rugged inner-string stimulation. Following a mutual crescendo with every string imaginable stroked, plucked, stopped, scraped or scrubbed, the two settle into a finale of minutely expressed plinks and plucks. The basic human affiliation on “Shaman” appears to vanish completely on “Ornamental” with the track mostly consisting of flutters and flanges, granular whizzes and blurry wiggles that appear to be processed as much from piano preparations and odd-guitar tuning as additional electronics. As the sound patterns constantly expand and deflate into atoms, a machine-like regularity is most prominent – fascinating in its way, but alienating as well.

Overall, although the point of the exercises is to create novel forms of timbral synthesis by subverting the expected sounds of the guitar and piano, those tracks which cunningly contrast the instruments’ acoustic and altered properties are most credible. Thus if the methodical keyboard centred piano line can be made out on “Harmony Dame” despite string vibrations and scrapes, the contrast is that mush more striking. Moreover when “Mad Rhyme”, the final track, climaxes with oscillated extensions from the many strings in play, the previous wood-and-metal distortions give way to rough yet authentic piano and guitar textures. Experimentation isn’t transformation. In this case the propriety of altering guitar and piano playing is made clearer when the acoustic antecedents are audible.

A similar showdown between electronic induced artificiality and pure instrumental tones exists on Alluvium. Except in this case, Minasi’s plectrum skills more appropriately link to the mainstream. Someone who began his career with major label exposure, the veteran guitarist’s has maintained a transformative approach to standards alongside more experimental forays. Nevertheless, although many of the improvisations appear to centre on spaces created when guitarists play high up on the neck, beneath the bridge, and use slurred fingering, the underlying continuum and daring finger picking are far removed from electronic interface or preparations. The final four selections – including the last “Rapid erosion” which includes wordless metrical chanting from one player – are cast in the relaxed mode. This sequence would never be confused with one involving Joe Pass and Herb Ellis, the plectrumists’ breakneck runs and chunky rhythms wed them to the Jazz tradition.

More crucially, no matter how many neck hand taps or percussive rasgueado is exposed, every tone is related to the instrument. Unlike Tammen’s and Maroney’s raison d’être, Tammen and Minasi never deny the sheer guitar-ness of the guitar.

The brief “Silt” for instance manages to explore the dynamic limits of crunches and strums while remaining a sensitive duet. Scrapped, spun and rippling string pressure exposed on “Finger Dance” still allows the two to downshift to easygoing swing; while a tune such as “Sand and Rain” casts them in classic guitar duo stance, as one flat-picks the melody and the other creates the accompanying ostinato. “Chasing Bulls” and “Don’t Look Back” may be the most overtly avant-garde of the duets, but throughout both guitar lines are deconstructed not endangered. Although stick-on-neck whacks are audible, the strangest tones heard are squeals that sound as if their source is horns rather than guitars.

Guitar fanciers of every stripe should be (come) familiar with Tammens’s work. Each of these CDs demonstrates that his playing can fascinate whether in a quasi-traditional string duo or using add-ons to jaggedly dismantle expected timbres.